1. Field of the Invention
The invention relates to a developing apparatus usable in an image forming apparatus such as a copying machine, a printer or a facsimile apparatus.
2. Description of the Related Art
An image forming apparatus adopting a conventional electrophotographic printing method will first be described with reference to FIG. 4 of the accompanying drawings.
As shown in FIG. 4 of the accompanying drawings, a popular image forming apparatus comprises a photosensitive member 101 as a rotatable latent image bearing member, a charging device 102 driven to rotate by the photosensitive member 101 for charging the photosensitive member 101 to predetermined potential, an exposing device 103 for forming an electrostatic latent image on the photosensitive member 101, a developing apparatus 104 for developing and visualizing the electrostatic latent image on the photosensitive member 101, a transferring device 105 for transferring the visible image on the photosensitive member 101 to a sheet, a fixing device 108 for fixing the visible image as a permanent image, and a cleaning device 106 for collecting any developer not transferred to the sheet but residual on the photosensitive member 101.
In recent years, there has been provided an image forming apparatus in which among these, the photosensitive member 101, the charging device 102, the developing apparatus 104 and the cleaning device 106 are integrally incorporated and made into a process cartridge detachably mountable on an image forming apparatus main body, whereby which is free of the necessity of maintenance and excellent in usability.
When the image forming apparatus shown in FIG. 4 is to be manufactured, in the step of assembling the developing apparatus comprised of at least the developer (hereinafter referred to as the toner) 111, a developer carrying member (hereinafter referred to as the developing sleeve) 110 carrying the toner 111 thereon, and a developer regulating member (hereinafter referred to as the developing blade) 109 for regulating a toner coating on the developing sleeve 110, it is generally practised to rotate the developing sleeve 110 for a predetermined time with the developing sleeve 110 not coated with the toner, with a view to effect the check-up of the quality such as appearance inspection.
At this time, however, it is feared that friction injuries are formed on the developing blade 109 and the developing sleeve 110, or if the developing blade 109 is formed of an elastic material such as urethane rubber, the developing blade 109 will be turned up in the rotation direction of the developing sleeve 110 by the frictional resistance between the developing blade 109 and the developing sleeve 110.
When such a product is put on the market and the use thereof by the use of the toner 111 is actually started, there is the possibility of uniform and good toner coating being not done on the developing sleeve 110.
In order to solve this problem, it is practised to apply a lubricant on that side of the developing blade 109 which abuts against the developing sleeve 110 when at the assembling step, the developing sleeve 110 is rotated for the predetermined time with the developing sleeve not coated with the toner 111.
The lubricant used at this time is related to the developing characteristic and the occurrence of development streaks at the initial stage whereat the developing sleeve 110 has been coated with the toner 111 and the developing apparatus has begun to be actually used and therefore, a lubricant having a proper charging characteristic, shape, etc. is selected and used.
For example, in Japanese Patent Application Laid-open No. H8-211728, there is proposed a method of applying spherical silicone resin particles having an average particle diameter of 5-30 μm in the form of a powder material onto the developing sleeve, and in Japanese Patent Application Laid-open No. H11-119551, there is proposed a method of applying resin particles having an average particle diameter of 5-45 μm and having a proper charge amount (spherical PMMA (polymethyl methacrylate), urethane, acryl, polystyrene or PVDF (polyvinylidene fluoride)), or amorphous silicone resin particles.
Also, recently, in Japanese Patent Application Laid-open No. 2002-278262, there has been done the proposition to adopt spherical polymer particles having an average degree of circularity of 0.90 or greater, and in which the application amount of lubricant in a longitudinal direction existing on a developer regulating member and a developer carrying member is 0.23-1.4 mg/cm, and of which the weight average particle diameter is greater than the surface roughness Rz of the developer carrying member.
Now, in a new (unused) developing apparatus, the toner in a developer container has charges not imparted thereto and therefore, even if charges are imparted by that portion of the developing blade which abuts against the developing sleeve, it is difficult for the proper charges of the toner to be immediately reached. Consequently, at the stage of beginning to use, a sufficient developing property is sometimes not obtained and density is low, or characters become thin.
Further, a ghost phenomenon due to the deficiency of charges imparted to the toner also appears.
The ghost phenomenon in this case is such that as shown in FIG. 5, the residual image of an image before one revolution of the developing sleeve 110 appears as a ghost image.
Particularly at the early stage of the use of the developing apparatus, if the regular charging polarity of the toner is the negative polarity, the negative ghost that the image becomes dark in the first one revolution of the developing sleeve and becomes light in the second and subsequent revolutions. This is because the toner on the developing sleeve after the toner has been used for development cannot immediately a proper charge amount and a proper coat amount and therefore, the developing property in the second and subsequent revolutions lowers and the negative ghost occurs.
Against this problem, the charging characteristic of the toner itself can be raised so that proper toner charges may be obtained, and the developing property can be set to a high level from the early stage of the use of the developing apparatus, but at the later stage (the latter half) of the use of the developing apparatus whereat the toner reaches the end of its life, a reduction in density often caused conversely by the excessive charge imparting of the toner.
There is also means for detecting only the early stage of the use of the developing apparatus and changing the setting of the developing bias of the image forming apparatus main body to a side for enhancing the developing property to thereby heighten the density, but by this means, it is impossible to eliminate the density difference between the first one revolution and the second and subsequent revolutions of the developing sleeve, and the effect for the ghost phenomenon is small.
Here, it has been found by the inventor's diligent study that the proposition of Japanese Patent Application Laid-open No. H3-191370 to provide a particle layer chargeable in a polarity opposite to a polarity of the developer to give the charge imparting effect of the developer is also effective to mitigate the negative ghost. This means was very effective against the negative ghost, but it has been found by the inventor's repeated study that when a toner having relatively high chargeability is used, a faulty image such as white haze or a longitudinal streak may occur.
In the toner having relatively high chargeability, if use is made of a lubricant consisting of only polymer particles of the opposite polarity, when the charge amount difference of the toner between a portion in which the toner and spherical polymer particles of the opposite polarity strongly contact with each other and a portion in which they weakly contact with each other or are in non-contact with each other becomes great and becomes non-uniform, development is effected in conformity with the chargeability and an uneven image or a hazy image is formed.